I think in part it is because "PM" is such a nebulous role, there isn't a clear career track for someone to become a PM so you end up with a widely disparate se

I think in part it is because "PM" is such a nebulous role, there isn't a clear career track for someone to become a PM so you end up with a widely disparate set of skills in that role. The best PM I worked with did comp-sci, decided he hated programming and went into project management, he got it. The worst was promoted out of customer support and didn't have a fucking clue.